Effects of landscape patterns of fire severity on regenerating ponderosa pine forests (<Emphasis Type="Italic">Pinus ponderosa</Emphasis>) in New Mexico and Arizona,USA |
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Authors: | Sandra L Haire Kevin McGarigal |
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Institution: | (1) Department of Natural Resources Conservation, Holdsworth Natural Resources Center, University of Massachusetts, Amherst, MA 01003, USA |
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Abstract: | Much of the current effort to restore southwestern ponderosa pine forests to historical conditions is predicated upon assumptions
regarding the catastrophic effects of large fires that are now defining a new fire regime. To determine how spatial characteristics
influence the process of ponderosa pine regeneration under this new regime, we mapped the spatial patterns of severity at
areas that burned in 1960 (Saddle Mountain, AZ) and (La Mesa, NM) 1977 using pre- and post-fire aerial photography, and quantified
characteristics of pine regeneration at sample plots in areas where all trees were killed by the fire event. We used generalized
linear models to determine the relationship of ponderosa pine stem density to three spatial burn pattern metrics: (1) distance
to nearest edge of lower severity; (2) neighborhood severity, measured at varying spatial scales, and (3) scaled seed dispersal
kernel surfaces. Pine regeneration corresponded most closely with particular scales of measurement in both seed dispersal
kernel and neighborhood severity. Spatial patterns of burning remained important to understanding regeneration even after
consideration of subsequent disturbance and other environmental variables, with the exception of a few cases in which simpler
models were equally well-supported by the data. Analysis of tree ages revealed slow progress in early post-fire years. Our
observations suggest that populations spread in a moving front, as well as by remotely dispersed individuals. Based on our
results, recent large fires cannot be summarily dismissed as catastrophic. We conclude that management should focus on the
value and natural recovery of post-fire landscapes. Further, process centered restoration efforts could utilize our findings
in formulating reference dynamics under a changing fire regime. |
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